Kerr--Newman Memory Effect

TL;DR

This paper investigates the gravitational memory effect at Kerr--Newman black hole horizons caused by shock waves, analyzing supertranslation charges at infinity and near-horizon limits, including electromagnetic interactions.

Contribution

It introduces a method to analyze the memory effect in Kerr--Newman spacetime using Bondi--Sachs gauge and compares horizon and null infinity perspectives.

Findings

Memory effect induces supertranslation charge changes.

Supertransformation charges are computed at horizon and infinity.

Electromagnetic field interactions with black hole angular momentum are explored.

Abstract

We bring the Kerr--Newman spacetime into the Bondi--Sachs gauge by means of zero angular momentum, null geodesics. We compute the memory effect produced at the black hole horizon by a transient gravitational shock wave, which from future null infinity is seen as a Bondi-Metzner-Sachs supertranslation. This results in a change of the supertransformation charges at infinity between the spacetime geometries defined by the black hole before, and after, the shockwave scattering. For an extremal Kerr--Newman black hole, we give the complementary description of this process in the near-horizon limit, as seen by an observer hovering over the horizon. In this limit, we compute the supertranformation charges and compare them to those calculated at null infinity. We analyze the effect of these transformations on the electromagnetic gauge field and explore the self-interaction between this and the angular momentum of the black hole.